Vacuum bag techniques are well known in the art of making large composites, such as those used in the manufacture of industrial containers and boats. They can involve both dry lay-up and wet lay-up processes. After the fiber reinforcement is laid up on a forming tool or mold surface, a flexible gas impervious sheet, liner, membrane or bag (hereinafter “bag”), is used to form a sealed vacuum envelope over the lay-up. A heat, ambient temperature or light curable catalyzed resin in liquid form is then introduced into the envelope and a vacuum is drawn on the interior envelope space. The vacuum induces an internal collapse of the film envelope against the mold surface and fiber reinforcement so that the resin and reinforcement follow the mold pattern and air pockets and voids are removed. Thereafter, the resin is cured by heat, ambient temperature or UV or ambient light.
Since the bag material restricts the resin from freely flowing though the fiber reinforcement, it has a tendency to trap air and other vapors between the vacuum bag film and the composite structure, a breather fabric with a plastic film which is positioned between the dry lay-up and the inside of the vacuum bag is used to prevent resin from reaching and plugging the vacuum lines in the bag. The breather bag functions to prevent the outer bag from collapsing completely on the lay-up. In addition, a resin distribution medium comprising space-apart plastic protrusions or monofilaments can be used to help distribute the resin without the entrainment of air or other gasses. Such as disclosed in Seemann U.S. Pat. Nos. 5,702,633; 4,902,215; 5,316,462 and 5,052,906, which are hereby incorporated by reference.
Vacuum bags are typically airtight films such as nylon or polyester, for example. One such material, called Quick Draw textured film (polyester thermoplastic Mylar) is transparent to UV light for UV-curable resin systems. Quick Draw film has been used in the preparation of boat hulls as disclosed in Livesay, et al., U.S. Pat. No. 5,837,185, also hereby incorporated by reference. The vacuum bag is discarded after each use. Permanent rubber bags, such as silicone or synthetic rubber have been used by some fabricators, but their high initial cost and handling and storage requirements result in limited and infrequent use by most commercial establishments. Silicone bags are also readily attacked by resin systems used to mold parts. In some cases, artisans have been known to add PTFE films to help overcome resin degradation of silicone bags, but this has been at great cost.
A vacuum bag is usually significantly oversized and has numerous folds so that bridging, or stretching, of the film over an angular area, such as a radius or sharp corner, is eliminated. If bridging occurs, the bag may rupture at high temperature and pressure causing the loss of the part. Vacuum bags are often used with separate non-stick release films and a mold release to prevent the parts from sticking to the tools and to the vacuum bag. The necessity of having both a polymeric vacuum bag film and an additional nonstick release film, as well as a chemical mold release, adds to the cost of bagging operations generally, and resin transfer molding operations in particular. Accordingly, there remains a need in the composites fabrication industry for a reusable vacuum bag which is cost-efficient, and which can withstand multiple mold cycles of a vacuum without significant leakage.